The disclosed technology relates to a semiconductor laser device and electronic equipment.
In a semiconductor laser device, conventionally, a heat sink is used for prevention of deterioration in emission efficiency, damage of a semiconductor laser element or the like due to temperature increases of the semiconductor laser element during operation of the laser. That is, a heat sink is bonded to a lower face of the semiconductor laser element via a solder layer so that heat generated during the operation is radiated efficiently from the heat sink.
However, stress occurs due to a difference in coefficient of thermal expansion between the semiconductor laser element and the heat sink, causing internal stress to occur to the semiconductor laser element. As a result, there is a problem that strain occurs to semiconductor layers forming the semiconductor laser element.
In view of such a problem, there has been proposed a semiconductor laser device of a prior art which is intended to reduce the internal stress of the semiconductor laser element depending on the electrode configuration of the semiconductor laser element (JP 3461632 B).
This prior-art semiconductor laser device 1, as shown in a sectional view of FIG. 3, has a semiconductor laser element 2, a solder layer 4 and a heat sink 5. The semiconductor laser element 2 is mounted on the heat sink 5 via the solder layer 4. The heat sink 5 has a heat sink member 8, an upper-face electrode 6 formed on one surface of the heat sink member 8 as viewed in its thicknesswise direction, and a lower-face electrode 7 formed on the other surface in the thicknesswise direction. The solder layer 4 is stacked on the upper-face electrode 6. Then, the semiconductor laser element 2 is stacked on the solder layer 4, to which an alloyed layer 19 forming a lower-face electrode 3 of the semiconductor laser element 2 is opposed.
In this semiconductor laser element 2, an active layer 13, a cap layer 15, an ohmic electrode layer 16 and a non-alloyed layer 17 are stacked in this order on one thicknesswise surface of a substrate 11. Meanwhile, an upper-face electrode 18 of the semiconductor laser element 2 is formed on the other thicknesswise surface of the substrate 11. Then, the alloyed layer 19 is stacked partly on the non-alloyed layer 17. The alloyed layer 19 and the non-alloyed layer 17 constitute the lower-face electrode 3.
As shown in FIG. 3, over a region 21 ranging to a specified length from a center line J0 of a light-emitting region 8 of the semiconductor laser element 2 in a perpendicular direction, perpendicular to a direction in which the light-emitting region 8 of the semiconductor laser element 2 extends in a stripe form (i.e. to a direction perpendicular to the drawing sheet) as well as perpendicular to the thicknesswise direction of the light-emitting region 8, toward both sides of the perpendicular direction, the alloyed layer 19 is absent and the non-alloyed electrode layer 17 is present. That is, in the region 21, the lower-face electrode 3 of the semiconductor laser element 2 is not alloyed with the solder layer 4, with the non-alloyed layer 17 confronting the solder layer 4. Meanwhile, in regions which are more distant from the center line J0 in the perpendicular direction than the region 21, the lower-face electrode 3 is alloyed with the solder layer 4, with the alloyed electrode layer 19 bonded to the solder layer 4.
When the semiconductor laser element 2 is thermally fused with the heat sink 5 via a solder material, the alloyed layer 19 of FIG. 3 comes to be alloyed with the solder material stacked on the heat sink 5 so as to be strongly bonded to the solder layer 4. In contrast to this, the non-alloyed layer 17 does not come to be alloyed with the solder material stacked on the heat sink 5, thus not being strongly bonded to the solder layer 4.
As a consequence, the internal stress is reduced in the non-alloyed layer 17 more than in the alloyed layer 19. Then, since the light-emitting region 8 is formed in a non-alloyed region, where the non-alloyed layer 17 is in contact with the solder layer 4, internal stress applied to the light-emitting region 8 can be reduced so that the semiconductor laser device 1 can be enhanced in its reliability.
In another aspect of the prior-art semiconductor laser device 1, since the non-alloyed layer 17 is formed just under the light-emitting region 8 of the semiconductor laser element 2, stress occurs to the light-emitting region 8 due to differences in coefficient of thermal expansion between the non-alloyed layer 17 and the ohmic electrode layer (alloyed layer 19) or the active region (light-emitting region 8), resulting in another problem that the reliability enhancement effect cannot be sufficiently obtained.